Among the various conventionally-known machine frames employed in multi-head sewing machines provided with a plurality of machine heads is a type disclosed, for example, in Japanese Patent Application Laid-open Publication No. HEI-9-94367. As shown in FIGS. 12 and 13, the disclosed sewing machine frame includes a pair of bases 20 opposed to each other, in a left-and-right direction (i.e., direction of arrow X), with a predetermined spacing interposed therebetween, and a pair of vertical supporting posts 21 fixed to the supper surfaces of the bases 20. Upper and lower frames 22 and 23 connect between and are fixed at opposite ends to the supporting posts 21; the upper frame 22 formed of a high-rigidity material, such as a rectangular steel pipe, is provided for mounting thereon machine heads (not shown) that drive sewing needles, while the lower frame 23 formed of a rectangular steel pipe or the like is provided for mounting thereon hook bases (not shown) each having a built-in rotary hook rotationally driven beneath the upper frame 22 in synchronism with up-and-down movement of a corresponding sewing needle. Auxiliary supporting posts 24 are fixed to the respective back surfaces of the two supporting posts 21, so as to strengthen joints between the bases 20 and the supporting posts 21 and between the supporting posts 21 and the upper frame 22.
The aforementioned sewing machine frame is assembled with respective fixed portions of its individual component parts welded together. Briefing a method for assembling and processing the conventionally-known sewing machine frame, a pair of leg sections A are formed by welding the supporting posts 21 and auxiliary supporting posts 24 to the bases 20, as illustrated in FIG. 13. Then, the upper frame 22 is placed on and welded to the upper end surfaces (indicated at A1 in the figure) of the thus-formed leg sections A, and the lower frame 23 is welded at its opposite end portions to respective vertically-intermediate portions (indicated at A2 in the figure) of the supporting posts 21. In this way, the upper and lower frames 22 and 23 connect between and are fixed at its opposite ends to the pair of leg sections A each comprising the base 20, supporting post 21 and auxiliary supporting post 24; namely, the sewing machine frame is assembled with the individual component parts integrally fixed together.
Such a sewing machine frame is pre-assembled as an integral unit, in a welding plant or the like, in the manner as described above. The thus pre-assembled sewing machine frame is transported to a machine assembling plant. In the machine assembling plant, other necessary component parts, such as machine heads, are assembled or attached to the transported sewing machine frame to ultimately complete a multi-head sewing machine. However, because the conventional sewing machine frames are each pre-assembled as an integral unit, many such pre-assembled sewing machine frames can not be transported at a time from the welding plant to the assembling plant, which undesirably results in a poor transport efficiency and hence an increase in the cost for transporting the sewing machine frames. Particularly, in cases where assembled sewing machine frames are transported to or from abroad, the aforementioned inconveniences would become prominent due to a packaging problem. As one approach to solve such problems, it is conceivable to separately pack the pair of leg sections A, upper frame 22 and lower frame 23 of each sewing machine frame and transport the separately-packed component parts to the machine assembling plant where the component parts are welded together to assemble the sewing machine frame. However, with the conventional sewing machine frame, the upper frame 22 and lower frame 23 have to be welded to different predetermined portions of the pair of leg sections A, which would require a long time. Besides, it is very difficult to weld the lower frame 23 accurately to the predetermined portions A2 of the leg sections A. Because of these, sewing machine frames can not be assembled appropriately in the machine assembling plant. Therefore, the above-mentioned approach can not be used appropriately, and, after all, there was no other choice but to transport sewing machine frames, pre-assembled in the welding plant, to the machine assembling plant.